1. Technical Field
The present invention relates to an improved seal, more particularly a supporting frame seal, which is optimised in terms of the determination and observance of positioning and assembly tolerances, as well as a corresponding production method.
2. Related Art
In the field of supporting frame seals there are more and more systems in which seals are joined to other components and then supplied to the assembly belt as a system or module. To connect, for example, supporting frame seals with metal oil sumps elastomer pins are moulded onto the supporting frames and are then pressed into corresponding openings in the metal oil sump.
As in newer systems the components and thereby the flange surfaces are steadily becoming smaller, all avoidable system tolerances have to be eliminated. These tolerances could lead to seal which has been assembled and supplied as component with an oil sump no longer resting completely on the housing of the component flange as a result of which leaks could occur. In order to keep the system tolerances as small as possible, the requirement is therefore that all system components, e.g. seals and the oil sump, have jointly corresponding fixing points or zero points. Ideally the components are then attached to each other at these zero points so that further tolerances can be eliminated and thereby additional tolerance chains avoided.
At present this requirement cannot be rationally implemented in certain types of sealing modules (e.g. metal oil sumps with a supporting frame seal and elastomer fixation pins). The problem is that basically the central point of an elastomer assembly pin should be selected as the zero point of the seal. In order to obtain minimum system tolerances, for the dimensioning and tolerancing of the hole pattern and flange surface opening of the oil sump a centring pin of the seal and an opening in the oil sump into which the centring pin is inserted are required as the zero point.
If the elastomer pin is selected as the zero point, this results in the metrological problem that the elastomer pin usually has a relatively small diameter and is of course naturally flexible as it is made of elastomer. In addition, influences such as material shrinkage and deformation make alignment on the elastomer pin very difficult and call into question the measurement of the entire component.
If, on the other hand, a screw opening in the metal support is selected as the zero point the component (essentially the hole pattern and thus the position of the sealing lips) can be metrologically recorded very well, though there is then an additional measuring section with tolerance to the moulded-on elastomer pin which often cannot be accepted because of the small flange overlap.
In both variants the following problem exists in connection with the metal supporting frame: during the production of the metal supporting frame it can only be rational to select the identical zero point for production and subsequent measuring of the component. Only in this way are there minimum deviations. The problem is that in the case of the known embodiments the pin is moulded into the metal surface of the supporting frame. Here, a channel is generally engraved via which the pin is filled with elastomer. The center point of the pin lies above this surface or on the supporting frame on this engraved surface. If the center is defined at this point it cannot in principle be measured on the component as graphically it is defined on a flat surface and thus lies on a metal surface.
It is known that in the case of components in which additional tolerances are not acceptable it is nevertheless decided to place the zero point on the pin, even if the evident metrological definition can subsequently lead to problems and the result is not always clear. So that the corresponding hole patterns in the case of supporting frame seals can be clearly measured, a zero point is then after all selected on the supporting frame in one of the screw holes close to the centring pin, even if this is not the optimum solution. The risk of selecting a metrologically not clearly definable zero point on the component, and the problem resulting from this of having a metrologically only inadequately determined and verifiable hold pattern on the supporting frame should be seen as a major problem in known components.